JPH07135612A - Picture signal converter, sstv signal demodulator and video signal demodulator - Google Patents

Abstract

PURPOSE:To obtain a picture signal converter by which an SSTV signal is demodulated with excellent S/N and linearity. CONSTITUTION:A received analog SSTV(Slow Scan Television) signal is given to an AGC circuit 4, in which its signal level is made almost constant, the resulting signal is converted into a digital signal at an A/D converter 6 and the digital signal is read in by a DSP(Digital Signal Processor) 7. The angular frequency of the SSTV signal is calculated in the DSP 7 according to the signal processing program read out of a ROM 8 and the change in the angular frequency per unit time is calculated. Thus, the SSTV signal is demodulated and the demodulated signal is stored in a video frame memory 9 and reproduced into an analog signal at a composite encoder 10 and the reproduced signal is monitored by a monitor television receiver 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal converter and a demodulator used in the image signal converter, and more particularly to demodulation of SSTV (Slow Scan Television) signals and conversion of video signals into SSTV signals. The present invention relates to an image signal conversion device for performing the above, an SSTV signal demodulation device for demodulating an SSTV signal, and a video signal demodulation device for demodulating a video signal as a still image.

[0002]

2. Description of the Related Art SSTV is one means of image communication by a low-speed scanning screen, and since an image signal is an SCFM signal, it has a smaller bandwidth than an ordinary television signal. It is often used in wireless communication. By the way, the output signal of a video camera used in SSTV is generally a so-called composite NTSC signal, and in order to transmit as an SSTV signal, it is necessary to convert such a video signal into a signal format conforming to the SSTV standard. is there. Also, in order to watch SSTV signals on a television receiver having a video terminal input,
On the contrary, it is necessary to convert to an NTSC signal, and as a device that fulfills such a function, there is an SSTV signal conversion device which is commonly called a so-called scan converter.

In a typical configuration of such a conventional SSTV signal conversion device, first, the output signal of the video camera is SS
In the portion for converting to a TV signal, a composite video signal which is an output signal of a video camera demodulates a color signal, a luminance signal, and a synchronizing signal in an analog state, an analog RGB signal is extracted from the luminance signal and the color signal, and then, This analog RGB signal is converted into a digital signal and stored in a video memory, and if necessary, taken out from the memory, converted into an analog signal, and then converted into an SSTV signal.

As another configuration, there is a configuration in which a composite signal is taken into a memory with a sampling clock having a subcarrier of the composite signal or a cycle of an integral multiple thereof. On the other hand, demodulation of the SSTV signal is generally performed by first passing the SSTV signal through a limiter and detecting a zero cross point.

[0005]

However, in the structure in which the composite signal is once decomposed into an analog RGB signal and then converted into a digital signal and stored in the memory as described above, the scale of the circuit becomes large, There is a problem that it becomes an expensive device. Also, if a heterodyne type VTR output signal in which the time base error has not been corrected by the time base collector is captured by a conventional device and a signal synchronized with the subcarrier is used for sampling, jitter will occur in the image, so be sure to use the time base. There was a problem that it could only be handled through the collector.

Further, in the conventional device, the SSTV signal is demodulated after the level is made uniform through a limiter.
It was designed to use zero-crossing detection, which performs demodulation by detecting the zero-cross point, but when the signal input to the limiter is weak, the level balance of the limiter affects the S / N ratio. There was a problem that demodulation with a good ratio would be difficult. Furthermore, since the demodulated signal obtained through the limiter is not suitable for digital linear signal processing, there is a problem that the demodulated signal cannot be digitally processed.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image signal conversion apparatus capable of performing digital signal processing without temporarily decomposing a composite signal into an analog RGB signal. . Another object of the present invention is to provide an image signal conversion device capable of obtaining a stable reproduced image even with a heterodyne VTR signal that does not pass through a time base collector. Furthermore, another object of the present invention is to provide a weak SST.
An object of the present invention is to provide an image signal conversion device capable of stably and reliably demodulating a V signal. Still another object of the present invention is SSTV without the use of conventional limiters.
An object is to provide an image signal conversion device capable of demodulating a signal.

[0008]

According to a first aspect of the present invention, there is provided an image signal conversion apparatus, wherein at least an analog / digital conversion means for converting a low speed scanning analog television signal into a digital signal, and the analog / digital conversion means. Demodulating means for demodulating image information from the output signal of the converting means, and the input level adjusting means for setting the input level of the analog television signal of the low speed scanning system in a substantially constant range, the analog / digital converting means. It is provided before the means. In particular, the input level adjusting means includes a voltage variable gain amplifier whose amplification degree changes according to an externally input gain control voltage signal, and a voltage signal corresponding to the average level of the input signal, which is a gain control signal of the voltage variable gain amplifier. And a mean level detector for outputting as. Also, especially
The demodulation means includes an angular frequency detection means for detecting an angular frequency of a television signal of a low speed scanning system from an output signal of the analog / digital conversion means, and an amount of change in the angular frequency detected by the angular frequency detection means per unit time. And a change amount detecting means for detecting

In the SSTV signal demodulating device according to the third aspect of the present invention, at least a voltage variable gain amplifier whose amplification degree changes according to a gain controlling voltage signal input externally and a voltage signal corresponding to the average level of the input signal. Is output as a gain control signal of the voltage variable gain amplifier.

According to a fifth aspect of the present invention, there is provided an SSTV signal demodulating device, wherein at least an analog / digital converting means for converting a low speed scanning type analog television signal into a digital signal and an output signal of the analog / digital converting means. Hilbert transforming means for performing Hilbert transforming, first delaying means for delaying the output signal of the analog / digital converting means by the same amount of delay as the delay time for the input signal of the Hilbert transforming means, and the Hilbert transforming means. Phase angle detecting means for calculating an arctangent of a ratio between the output signal of the first delay means and the output signal of the first delay means to generate a signal corresponding to the angular frequency of the television signal of the low speed scanning system, Second delaying means for delaying an output signal of the phase angle detecting means by a fixed time; Those formed by anda phase angle change detecting means for detecting a frequency change of the television signal of the low-speed scanning method by the difference between the output signal and the output signal of the phase angle detection means of the delay means.

According to a sixth aspect of the present invention, there is provided an image conversion apparatus, wherein at least first analog / digital conversion means for converting a low speed scanning analog television signal into a digital signal, and the first analog / digital conversion means. Demodulation means for demodulating image information from the output signal of the means,
Second analog / digital conversion means for converting the analog composite video signal into a digital signal asynchronously with the color subcarrier signal included in the video signal, and storing and holding the signal of the second analog / digital conversion means. A memory holding means for rewriting the stored and held data to the digital component video signal when a digital component video signal is inputted from the outside, and a chroma signal extracting a chroma signal component from the signal read from the memory holding means. An output signal of the chroma signal extraction means; a first delay means for delaying the output signal of the storage holding means by the same amount of delay as the delay time with respect to the input signal of the chroma signal extraction means; Y / C component for extracting a luminance signal from the output signal of the first delay means Means, a Hilbert transform means for subjecting the output signal of the chroma signal extraction means to a Hilbert transform, and a delay of the same amount as the delay time with respect to the input signal of the Hilbert transform means for the output signal of the chroma signal extraction means. A burst signal included in the analog composite video signal from the second delay means, the output signal of the Y / C separation means, the output signal of the Hilbert conversion means, and the output signal of the second delay means. Phase calculating means for calculating a phase difference from the digital composite video signal digitally converted by the second analog / digital converting means, an output signal of the Hilbert converting means, and an output signal of the second delaying means, Chroma decoding means for extracting a color difference signal from the output signal of the phase calculating means, and the Y / C component An output signal of the means, and an output signal of the chroma decoding means, in which to calculate the component signals by matrix operation comprising anda matrix operation means for outputting to the memory holding means.

According to a seventh aspect of the present invention, there is provided a video signal converting apparatus, wherein the analog / digital converting means converts at least an analog composite video signal into a digital signal asynchronously with a synchronizing signal included in the video signal, and the analog / digital converting means. While storing and holding the signal of the means,
Storage holding means for rewriting the stored data to the digital component video signal when the digital component video signal is input from the outside,
Chroma signal extraction means for extracting a chroma signal component from the signal read out from the memory holding means, and a delay of the same amount as the delay time with respect to the input signal of the chroma signal extraction means for the output signal of the memory holding means. Y for extracting a luminance signal from the first delaying means for giving a luminance signal, the output signal of the chroma signal extracting means and the output signal of the first delaying means.
/ C separation means, a Hilbert transform means for subjecting the output signal of the chroma signal extraction means to a Hilbert transform, and an output signal of the chroma signal extraction means of the same delay time as the input signal of the Hilbert transform means. Second delay means for delaying, an output signal of the Y / C separation means, an output signal of the Hilbert conversion means, and the second signal
From the output signal of the delay means, the burst signal included in the analog composite video signal and the analog signal
Phase calculating means for calculating a phase difference from the digital composite video signal digitally converted by the digital converting means, and an output signal of the Hilbert converting means,
Chroma decoding means for extracting a color difference signal from the output signal of the second delay means and the output signal of the phase calculating means, the output signal of the Y / C separating means, and the output signal of the chroma decoding means. From the matrix calculation R
Matrix operation means for calculating the GB component signal and outputting it to the memory holding means.

[0013]

According to the first aspect of the invention, the level of the slow-scanning type television signal input in analog is set to a substantially constant range by the level adjusting means even if there is a large level change at the time of input. The digital linear processing after this becomes possible, and the conventional adjustment of the signal level by the limiter becomes unnecessary.

According to the third aspect of the invention, the level of the slow-scanning type television signal inputted in analog is an average level calculated by the average level detector even if there is a large level fluctuation at the time of input. By being amplified by the gain set by the voltage variable gain amplifier according to, it will be within a substantially constant range, and as a result,
Subsequent digital linear processing becomes easy.

In a fifth aspect of the present invention, the digital signalized low speed scanning type television signal is Hilbert-transformed by the Hilbert transforming means to be a signal having a phase difference of 90 degrees from the original signal, The angular frequency of the original signal is calculated by calculating the arc tangent with respect to the ratio of the signal that has passed through the Hilbert transformer and the signal that does not pass through the Hilbert transformer in the phase angle detector. Then, in order to detect the change in the angular frequency per unit time, the phase angle change detecting means includes a signal obtained by delaying the output signal of the phase angle detecting means for a fixed time and a phase angle detecting without delay. The output signal of the means is applied, and by calculating the difference between them, the change in the angular frequency is detected, and the demodulation of the television signal of the low speed scanning system is realized.

In the inventions of claims 6 and 7, the chroma signal is extracted by passing the digital signal-converted composite video signal through the chroma signal extraction means, and the chroma signal and the composite video signal digitized. Are applied to the Y / C separation means, and the difference is calculated, so that a luminance signal is obtained. Then, the phase calculating means calculates the sampling phase of the second analog / digital converting means from the luminance signal and the two chroma signals having a 90-degree phase difference by the Hilbert converting means. In the decoding means, a color difference signal is calculated from this phase and two chroma signals having a phase difference of 90 degrees with each other. Then, in the matrix calculation means, the component video signal is obtained as a result of performing the matrix calculation with the luminance signal and the color difference signal output from the chroma decoding means.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the invention described in claims 1 to 7 will be described below with reference to FIGS. Here, FIG. 1 is a block diagram showing an embodiment of an image signal conversion apparatus according to the invention described in claim 1, and FIG. 2 is an image signal conversion apparatus according to the invention described in claim 2 and the invention described in claim 3. FIG. 3 is a configuration diagram showing an embodiment of the SSTV signal demodulating device according to the present invention, and FIG. 3 is a configuration diagram showing an embodiment of the image signal converting device according to the invention according to claim 4 and the SSTV signal demodulating device according to the invention according to claim 5. ,
FIG. 4 is a block diagram showing an embodiment of the image signal conversion device according to the invention described in claim 6 and the video signal conversion device according to the invention described in claim 7, and FIG. 5 is for explaining the principle of extracting color difference signals. It is a vector diagram of. The members, arrangements, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.

First, the image signal converting apparatus will be described with reference to FIG. This image signal converter is an SSTV
The signal conversion unit 1 and the video signal conversion unit 2 are provided, and the SSTV signal conversion unit 1 is an SST input from the outside.
The signal processing necessary for displaying the V signal on the monitor TV receiver 3 is performed, while the video signal conversion unit 2 performs the signal processing necessary for displaying the video signal input from the outside on the monitor TV receiver 3. Together, this video signal is SS
It is to be converted into a TV signal.

The SSTV signal converter 1 (the part surrounded by the chain double-dashed line in FIG. 1) has an AGC circuit 4 as an input level adjusting means and a first low-pass filter (hereinafter referred to as "first LPF"). .) 5, an A / D converter 6 as digital / analog conversion means, a digital signal processing processor (hereinafter referred to as "DSP") 7, and a read-only memory (hereinafter referred to as "ROM") 8. , A video frame memory 9, a composite encoder 10,
It is configured to include. Incidentally, the A / D converter 6, the ROM 8 and the video frame memory 9 in the present embodiment.
The composite encoder 10 is configured to be commonly used with the video signal conversion unit 2 described later.

The AGC circuit 4 has an SS input from the outside.
Since the TV signal may be accompanied by level fluctuations, such level fluctuations are removed and output to the circuit in the subsequent stage as a substantially constant output level, whereby signal processing in the subsequent stage can be performed reliably and reliably. Like The first LPF 5 removes a false signal included in the SSTV signal,
This is a low-pass filter for obtaining the originally required SSTV signal. The A / D converter 6 converts the analog SSTV signal input via the first LPF 5 into a digital signal.

The DSP 7 is an I dedicated for digital signal processing.
This is a so-called C-coded processor, and although not shown, a multiplier, accumulator, ALU (Arithmetic and Logic)
Unit), RAM for data storage, I / O port, etc., instructions are microprogram-like, multiple instructions can be processed by one instruction, each instruction execution time is fast and it is executed in one machine cycle It is known and known per se.

The DSP 7 of the present embodiment executes the program written in the ROM 8 to perform the arithmetic processing necessary for accumulating the digital SSTV signal output from the A / D converter 6 in the video frame memory 9. The function of writing a digital video signal in the video frame memory 9 is fulfilled. Incidentally, the DSP 7 in this embodiment
Is also used as the video signal conversion unit 2 and constitutes a part of the video signal conversion unit 2 as described later.

The video frame memory 9 stores a digitized video signal, and in the present embodiment, it is possible to store signals for one screen. Of course, a field memory may be used instead of the video frame memory 9. And the composite encoder 1
0 is for converting the digital image signal output from the video frame memory 9 into an analog composite signal, and this output is input to the monitor TV receiver 3 so that it is displayed as a still screen. .
In the present embodiment, the DSP 7 and ROM 8 described above are used.
The video frame memory 9 constitutes demodulation means.

On the other hand, the video signal converter 2 (the portion surrounded by the alternate long and short dash line in FIG. 1) includes a buffer amplifier 11 and
A write timing generator 12, an A / D converter 6, a DSP 7, a video frame memory 9, a ROM 8 and a composite encoder 10, which are shared with the above-mentioned SSTV signal converter 1, a D / A converter 13, and a second. Low pass filter (hereinafter, referred to as “second LPF”) 14 of FIG. The buffer amplifier 11 buffers and amplifies the input video signal and outputs it to the A / D converter 6 and the write timing generator 12. And A / D
The converter 6 converts the input analog video signal into a digital signal and outputs it to the DSP 7.

The write timing generator 12 outputs the video signal digitized by the A / D converter 6 to the DSP 7
The timing and address required for writing to the video frame memory 9 via the buffer are generated based on the sync signal of the video signal input via the buffer amplifier 11 and input to the video frame memory 9. DSP7
Performs processing as described below on the video signal digitized by the A / D converter 6, and finally stores a so-called component video signal decomposed into RGB components into the video frame memory 9. It fulfills functions and the like.

Then, the RGB component video signals stored in the video frame memory 9 are read out as desired in the same manner as in the SSTV signal conversion section 1 described above, and are returned to analog video signals by the composite encoder 10. Thus, it can be displayed as a still image on the monitor TV receiver 3.

On the other hand, the D / A converter 13 inputs a signal read from the video frame memory 9 and converted into a digital SSTV signal by the DSP 7, as described later, and converts it into an analog SSTV signal. Is. Then, the second LPF 14 removes a false signal included in the D / A converted analog SSTV signal.

Next, the operation of the present apparatus having the above configuration will be described. First, the operation of this apparatus will be described generally. An SSTV signal is input and demodulated, and this is monitored by a monitor TV.
It has a function of outputting to the receiver 3 and a function of inputting a video signal and converting it to an SSTV signal and outputting it, and also a function of outputting the input video signal to the monitor TV receiver 3 as a still screen. It is what First, SS
Explaining the demodulation function of the TV signal, when the SSTV signal is input from the outside, the DSP 7 determines that the signal is an SSTV signal by a detection processing circuit (not shown). DS
It is switched to the contact A side by P7.

The SSTV signal input from the outside is the AG
In the C circuit 4, after the signal level is set to be substantially constant, the false signal is removed by the first LPF 5 and the changeover switch 1
It is input to the A / D converter 6 via 5. And A /
The D converter 6 converts the analog SSTV signal into a digital SSTV signal. This digital SSTV
The signals are taken into the DSP 7, converted into RGB component video signals there, and then written in the video frame memory 9.

R written in the video frame memory 9
The GB component video signal is sequentially read and input to the composite encoder 10 in accordance with the control instruction of the DSP 7. Then, it is converted into an analog video signal and input to the monitor TV receiver 3 so that it can be visually recognized as a still image.

Next, the operation of converting a video signal into an SSTV signal and the operation of outputting to the monitor TV receiver 3 will be described. When a composite video signal is input to this apparatus, the changeover switch 15 is automatically switched to the contact B side by the detection operation of the DSP 7, and the composite video signal is input. The input composite video signal is input to the A / D converter 6 through the buffer amplifier 11 and converted into a digital video signal, and the video frame memory 9 is temporarily synchronized with the timing generated by the write timing generator 12. Written in.

The digital video signal temporarily written in the video frame memory 9 is read into the DSP 7 and decoded into an RGB component video signal. Then, the RGB component video signal is written in the video frame memory 9 again by the DSP 7. Therefore, the data in the video frame memory 9 at this point is changed from the digital composite video signal to the RGB component video signal.

Then, the component video signals of RGB stored in the video frame memory 9 are read by the DSP 7 and input to the composite encoder 10, and a still image is displayed on the monitor TV receiver 3 as in the case of the SSTV signal. It is supposed to be projected as.

On the other hand, when a transmission start switch (not shown) is pressed, the above-mentioned RGB component video signals are read out from the video frame memory 9 under the control of the DSP 7 and read into the DSP 7. DS
Inside P7, the read RGB component video signals are modulated into digital SSTV signals and D /
Output to the A converter 13. And digital SSTV
The signal is converted into an analog SSTV signal by the D / A converter 13, and after the false signal is removed by the second LPF 14, the signal is output to the outside.

Next, an embodiment of the inventions set forth in claims 2 and 3 will be described with reference to FIG. First, this SST
Generally speaking, the function of the V signal demodulating device is such that the present device enables the subsequent digital linear signal processing by setting the SSTV signal input from the outside with the fluctuation of the signal level to a uniform signal level. To do. Then, this device corresponds to a portion composed of the AGC circuit 4, the first LPF 5 and the A / D converter 6 shown in FIG. 1, and in the device shown in FIG. It is also possible to replace the relevant part described above with this SSTV demodulator.

This SSTV signal demodulating device comprises a voltage variable gain amplifier 16, an average level detector 17, a low pass filter 18 and an A / D converter 19 (see FIG. 2). The low-pass filter 18 and the A / D converter 19 have basically the same configuration and function as the first LPF 5 and the A / D converter 6 described in FIG. 1, and therefore description thereof will be omitted here. I decided to.

The voltage variable gain amplifier 16 is such that its amplification degree is variable according to the voltage signal input from the average level detector 17. The average level detector 17 detects the average level of the input SSTV signal, and this detection voltage serves as a so-called AGC voltage for the voltage variable gain amplifier 16 described above. That is, the amplification degree of the voltage variable gain amplifier 16 is configured to decrease as the detection voltage of the average level detector 17 increases, and the voltage variable gain amplifier 16 and the average level detector 17 are so-called forwards. The AGC is configured.

By passing the SSTV signal through the voltage variable gain amplifier 16 as described above, even if the signal is weak at the time of input, the SSTV having a good S / N ratio is obtained as compared with the conventional case where the signal is passed through the limiter. A signal can be obtained, digital linear processing can be performed thereafter, and good demodulation is performed.

Further, a limiter is conventionally provided before A / D conversion, but in this case, even if an attempt is made to secure a wide dynamic range, there is a limit naturally, and either the high level input side or the low level input side is limited. Since I had to sacrifice to some extent and set the level, SSTV
If the signal is accompanied by relatively large fading, demodulation with good linearity could not be realized. On the other hand, since the limiter itself is not used in the demodulation device of the present embodiment, the conventional problem as described above does not occur, and highly accurate demodulation can be performed even with SSTV signals accompanied by fading. Will be seen.

FIG. 3 shows an embodiment of the invention described in claims 4 and 5, and this embodiment will be described below with reference to the same figure. First, the function of the SSTV signal demodulating device will be described generally.
The signal is digitized and the SSTV signal is demodulated in the digital domain. Further, this SSTV signal demodulating device corresponds to the device shown in FIG. 1 in which the demodulation processing portion which was performed by software using the DSP 7 is configured by so-called hardware. Of the SSTV converter 1 in the device
This SSTV signal demodulating device can replace the part excluding the SP 7, ROM 8 and video frame memory 6.

This SSTV signal demodulator is an analog / analog
A / D converter 20 as digital converting means, Hilbert filter 21 as Hilbert converting means, first delay element (described as "delay element" in FIG. 3) 22 as first delay means, and phase A phase angle detector 23 as an angle detecting means, a second delay element (described as “delay element” in FIG. 3) 24 as a second delay means,
And a phase angle change detector 25 as a phase angle detecting means. The A / D converter 20 converts the input analog SSTV signal into a digital SSTV signal, and the digitized SSTV signal is input to the Hilbert filter 21 and the first delay element 22, respectively. There is. In this embodiment, the Hilbert filter 21, the first delay element 22 and the phase angle detector 23 are the angular frequency detecting means of claim 4, and the second delay element 24 and the phase angle change detector 25 are the same. The change amount detecting means of claim 4 is configured respectively.

The Hilbert filter 21 is for shifting the phase of the input digital signal by 90 degrees. The first delay element 22 compensates for the signal delay generated in the Hilbert filter 21, and the digital SSTV signal passed through the Hilbert filter 21 and the Hilbert filter 2
The digital SSTV signal that does not pass 1 is input to the phase angle detector 23 at the same time.

The phase angle detector 23 inputs the signal passed through the Hilbert filter 21 and the signal passed through the first delay element 22, and calculates the arc tangent (Tan ^-1 ) from these two signals. By doing so, the phase angle of the signal is calculated (details will be described later). A part of the calculated phase angle signal is delayed by n samples by the second delay element 24 and input to the phase angle change detector 25,
A part of the phase angle change detector 2 does not pass through the second delay element 24.
5 is added directly (see FIG. 3).

The phase angle change detector 25 is the phase angle detector 2
By subtracting the output signal of the second delay element 24 from the output signal of No. 3, the change in the phase difference per unit time is calculated and the SSTV signal is demodulated.

Next, the principle of the SSTV signal demodulation from the calculation of the arc tangent in the phase angle detector 23 and the calculation processing in the phase angle change detector 25 will be described. First, it is assumed that the signal input to the Hilbert filter 21 is represented by y = Asin ωt (A is a constant representing amplitude, ω is angular frequency, and t is time). Also, if the output signal of the Hilbert filter 21 is x, this signal is obtained by shifting the phase of the previous input signal y by 90 degrees due to the Hilbert transform, so x =
It is expressed as Acos ωt.

Here, the ratio between the signal y and the signal x is expressed as follows. That is, y / x = Asin ωt / Aco
sωt = tan ωt, from which ωt = tan
^-1 (y / x) is obtained. Now, when the change Δω in the phase angle when a minute time Δt elapses with reference to a certain time t0,
Δω = ω (t0 + Δt) −ωt0 = ωΔt = tan ⁻¹ (y
1 / x1) -tan- ¹ (y0 / x0). In addition, y1, x1
Is the value of the signals y, x at time (t0 + Δt), y0, x
0 is the value of the signals y and x at time t0. And Δ
Since t is constant, the above Δω (the output of the phase angle detector 23) is proportional to the angular frequency ω of the input signal. Therefore, the SSTV signal is demodulated by detecting the change in the output signal of the phase angle detector 23 per unit time in the phase angle change detector 25.

The operation of the demodulator having the above-described structure will be generally described. First, the analog SSTV is input.
The signal is first converted into a digital signal in the A / D converter 20, and is input to the first delay element 22 and the Hilbert filter 21, respectively. Phase angle detector 23
, Two digital SSTV signals having a phase difference of 90 degrees from each other are arctangent (Ta
By calculating n ⁻¹ ), the phase angle is calculated and output as a voltage signal. Then, part of the output is input to the phase angle change detector 25, and part of the output is input to the phase angle change detector 25 after being delayed by the second delay element 24 for a predetermined time.

Then, in the phase angle change detector 25,
From the difference between the signal directly input from the phase angle detector 23 and the signal from the second delay element 24, the amount of change in the phase difference per unit time is calculated. The amount of change in the phase difference per unit time corresponds to that obtained by demodulating the SSTV signal,
After all, the demodulated signal of the SSTV signal is obtained as a digital signal at the output of the phase angle change detector 25.

As mentioned at the beginning, this device is
In the device shown in FIG. 1, the part of the demodulation process that was performed by software using the DSP 7 is equivalent to what is called hardware.
The corresponding part of the SSTV signal converter 1 in the device shown in FIG. 2 may be replaced with this SSTV signal demodulating device. Since the operation at that time is basically the same as the above-mentioned operation, the description thereof is omitted here.

FIG. 4 shows an embodiment of the invention described in claims 6 and 7, and this embodiment will be described below with reference to the same figure. First, the function of the video signal demodulating device shown in FIG. 4 will be described generally. This video signal demodulating device digitizes an externally input composite video signal into a video frame memory as a digital video signal for one frame. Is stored in the monitor TV receiver 3 so that it can be displayed as a still image on the monitor TV receiver 3.

This video signal demodulation device corresponds to the device shown in FIG. 1 in which the DSP 7 demodulation process of the video signal, which is performed by software, is configured by so-called hardware. The video signal demodulating device can replace the demodulation processing part of the video signal in the device shown in FIG.

This video signal demodulating device includes an A / D converter 26 as an analog / digital converting means, a write timing generator 27, a video frame memory 28, and a first delaying means as a first delaying means. An element (abbreviated as "delay element" in FIG. 4) 29 and a bandpass filter (hereinafter, referred to as "BPF") as a chroma signal extraction means.
30 and a Y / C separator 31 as Y / C separating means,
A second delay element (abbreviated as “delay element” in FIG. 4) 32 as a second delay means, a Hilbert filter 33 as a Hilbert conversion means, a phase calculator 34 as a phase calculation means, and a chroma decoding. A chroma decoder 35 as means, a matrix calculator 36 as matrix calculation means, a read timing generator 37, and a composite encoder 38 are provided. Among these components, the A / D converter 26, the write timing generator 27, the video frame memory 28, and the composite encoder 38 are the same as those shown in FIG.
Since the D converter 6, the write timing generator 12, the video frame memory 9 and the composite encoder 10) basically have the same functions, detailed description thereof will be omitted here. The Hilbert filter 33 is also shown in FIG.
Since the function is basically the same as that shown in FIG. 2, description thereof will be omitted here.

The BPF 30 is a video frame memory 28.
It is a bandpass filter for extracting a chroma signal modulated by a color subcarrier from the digital video signal read by the FIR (Finite impulse response)
system) type filter is used. The first delay element 29 is a delay element having the same delay amount as the delay time for the passing signal of the BPF 30 described above, and the digital video signal read from the video frame memory 28 and the chroma signal output from the BPF 30. It is provided for inputting and to the Y / C separator 31 without a time delay.

The Y / C separator 31 includes a first delay element 29.
The luminance signal Y is obtained by subtracting the chroma signal from the video signal input from the video frame memory 28 via the luminance signal Y. The luminance signal Y is input to the phase calculator 34 and the matrix calculator 36. Has become. The phase calculator 34 uses the luminance signal Y that is the output signal of the Y / C separator 31, the chroma signal that has passed through the second delay element 32, and the BPF 30 using the Hilbert filter 33.
And a chroma signal having a phase difference of 90 degrees with respect to the chroma signal output from the input signal. Then, the phase calculator 34, based on these input signals, regarding the phase angle ψ of the burst phase with respect to the sampling phase,
SINψ and COSψ are calculated (details will be described later).

The chroma decoder 35 inputs two chroma signals having a phase difference of 90 degrees to each other and SINψ and COSψ which are the outputs of the phase calculator 34, and demodulates the color difference signals U and V. (Details will be described later). The matrix calculator 36 inputs the luminance signal output from the Y / C separator 31 and the two color difference signals U and V output from the chroma decoder 35, and performs matrix calculation using these three signals. Then, the RGB component video signals are obtained (details will be described later). In the present embodiment, the write timing generator 27, the video frame memory 28 and the read timing generator 37 constitute a memory holding means.

Next, the operation of the present video signal demodulating device having the above configuration will be described. First, an analog composite video signal input from the outside is converted into a digital signal in the A / D converter 26, and written in the video frame memory 28 according to the write timing generated by the write timing generator 27. Therefore, the digital signal written in the video frame memory 28 includes not only the luminance signal and the chrominance signal but also the synchronization signal and the burst signal, and the composite video signal itself can be written as a digital signal. Has become. Further, the write timing generator 27 generates timing and address data for writing the output signal of the A / D converter 26 in the video frame memory 28 based on the synchronizing signal included in the composite video signal. The sampling frequency and phase used in this device are set asynchronously with those of the subcarriers included in the composite video signal. This is so that even a video signal output from a heterodyne type VTR can be directly input as will be described later.

After the digital composite video signal for one screen is input from the A / D converter 26 to the video frame memory 28, this signal is read again according to the timing generated by the read timing generator 37, 1
Are input to the delay element 29 and the BPF 30, respectively.
Then, in the Y / C separator 31, the first delay element 2
B from the composite video signal input via 9
By subtracting the chroma signal obtained by the PF 30, the luminance signal Y is obtained and input to the phase calculator 34 and the matrix calculator 36, respectively.

On the other hand, the chroma signal obtained from the BPF 30 is supplied to the phase calculator 34 and the chroma decoder 35 as two chroma signals having a phase difference of 90 degrees from each other by the second delay element 32 and the Hilbert filter 33. Is entered. Then, in the chroma decoder 35, this 2
Two chrominance signals U and V are demodulated from one chroma signal and the SIN and COS values regarding the phase angle of the burst phase with respect to the sampling phase input from the phase calculator 34 (details will be described later). .

Then, in the matrix calculator 36,
An RGB component video signal is obtained by performing a matrix operation from the luminance signal Y and the color difference signals U and V. And this component video signal is
It is written in the video frame memory 28, converted into a composite video signal by the composite encoder 38, and can be displayed as a still image on the monitor TV receiver 3.

Next, the operating principles of the phase calculator 34 and the chroma decoder 35 will be described in detail with reference to FIG. First, the A / D converter 26 of this embodiment performs sampling at a frequency that is four times the subcarrier frequency fsc of the composite video signal input from the outside, but this sampling signal is as described above. Since it is asynchronous with the subcarrier, a phase angle ψ (not constant but varying with each sampling) is generated with respect to the phase of the burst signal, as shown in FIG. 5A. In FIG. 5, B indicates a burst signal, and a indicates a component of the burst signal on the Q axis.

When the video signal having the phase angle ψ with respect to the burst phase passes through the Hilbert filter 33, the burst signal is 90 ° with respect to the phase at the time of FIG. 5A, as shown in FIG. 5B. The phase is delayed. still,
b is the component of B on the Q axis. Here, assuming that the sampling phase is at the position of X on the Q axis, the burst signal components a and b in the two orthogonal signals (I, Q) are obtained by the following equation. That is, a = B
sin ψ and b = B cos ψ.

Therefore, sin ψ = a / B, cos ψ
= B / B, but from the relationship of B = √ (a ² + b ² ), s
in ψ = a / √ (a ² + b ² ), cos ψ = b / √ (a ²
The sin ψ and cos ψ are calculated as + b ² ). In the present embodiment, in the phase calculator 34, from the luminance signal Y, the output signal of the second delay element 32 and the output signal of the Hilbert filter 33, the above sin ψ and cos ψ.
Is being calculated.

Also for the chroma signal, the I and Q axis components can be obtained by applying the Hilbert transform as in the case of the burst signal described above. Then, in order to detect this as the U and V axis components, it is necessary to perform the following processing. That is, to put it briefly, first, by rotating the I / Q axis shown in FIG. 5A by −ψ, the U and V axis components can be obtained from the I and Q axis components. Specifically, first, if the sampling value on the I axis is X and the sampling value on the Q axis is Y,
A vector quantity Z representing a chroma signal is expressed by a complex number expression Z
= X + iY.

On the other hand, if the values after converting the above X and Y to the U and V axes are respectively x and y, the vector quantity z representing the chroma signal in the U and V axis space is z = x.
It can be expressed as + iy. Therefore, as described above, the relational expression of z = Ze ⁻ⁱ ψ holds between the vector quantity Z and the vector quantity z having the phase angle ψ. Further, this relational expression can be expanded to z = Z (cos (−ψ) + isin (−ψ), and the following formula can be obtained by substituting the relational expressions representing the vector quantities Z and z. That is, x + iy
= (Xcosψ + Ysinψ) + i (Ycosψ−Xs
in ψ). If this is made into a matrix form, it becomes like the following formula 1.

[0065]

[Equation 1]

Cos ψ and sin ψ are obtained as the output of the phase calculator 34 as described above, and X
And Y are obtained as the output of the Hilbert filter 33 and the output of the second delay element 32, and the chroma decoder 35 performs the matrix operation shown in the above-mentioned expression 1 from these input signals. Then, x and y in the mathematical expression 1 become the color difference signals U and V which are the arithmetic output in the chroma decoder 35 (see FIG. 4).

In the video signal demodulating device according to this embodiment, the sampling signal is not intentionally synchronized with the burst as described above, so that TBC (Time Base Corecto) is used.
Even with a video signal of the heterodyne system that is input without passing through r), a stable image can be obtained without causing inconvenience such as image jitter in the monitor TV receiver 3. That is, the video signal of the heterodyne system has a drawback that the horizontal scanning frequency fluctuates in principle. Therefore, when the sampling signal is synchronized with the synchronization signal included in this video signal, the sampling frequency also changes, and the number of horizontal samples of the video signal read into the video frame memory 28 via the A / D converter 26 is reduced. At worst, there is a different fear for each line.

The image jitter is fluctuation of the screen which occurs when such video signals having different sampling numbers are reproduced. In the present embodiment, the sampling signal is not synchronized with the burst signal as described above. A stable still image can be reproduced even with the system video signal. This video signal demodulation device can directly capture even a video signal of the heterodyne system. Therefore, in order to avoid the problem caused by the fluctuation of the horizontal scanning frequency in the video signal of the heterodyne system, the time axis correction is performed. Performing TBC (Time Base Corector)
It is not necessary to pass through or to decompose into RGB in advance and then perform digital processing.

In this embodiment, the video frame memory 28 stores data for one screen,
Needless to say, it is not always necessary to store data for one screen, and data for several screens may be stored. Further, in the present embodiment, the RGB component video signals are stored and held in the video frame memory 28. However, the RGB component video signals are not necessarily required, and component video signals of other formats (for example, Y, U, V, etc.).

Further, as described at the beginning, this video signal demodulating device is the same as the device shown in FIG.
7 is equivalent to a so-called hardware-configured part of the video signal demodulation process that was performed by software, and the video signal demodulation process part in the device shown in FIG. It may be replaced by a video signal demodulating device. Since the operation at that time is basically the same as the above-mentioned operation, the description thereof is omitted here.

[0071]

According to the present invention, the level of the input low speed scanning type television signal is set within a substantially constant range, thereby eliminating the need for a limiter unlike the prior art. Therefore, it is possible to perform digital linear signal processing, and it is possible to perform demodulation with a good S / N ratio even for an input signal with a level change.

According to the invention of claim 4, the demodulation can be performed without using the conventional so-called zero-cross method, and the level of the input signal is substantially constant as in the inventions of claims 1 to 3. By configuring the range to be subjected to digital linear processing, problems such as deterioration of demodulation performance for a weak input signal and deterioration of S / N ratio, which have occurred in the conventional device due to the level balance of the limiter. It is possible to perform accurate demodulation even for an input signal having a wide deviation, and it is possible to perform demodulation with good linearity because a limiter is not used in the input stage.

According to the fifth aspect of the present invention, since the demodulation can be performed without using the conventional so-called zero-cross method, the demodulation can be performed with high precision even for an input signal having a wide deviation. Since the limiter is not used in the input stage, demodulation with good linearity can be achieved.

According to the sixth and seventh aspects of the invention, the input signal is converted into a digital signal asynchronously with the synchronizing signal of the input composite video signal, and in the subsequent demodulation processing, the difference between the burst signal and the sampling phase is obtained. Is calculated and the value is used to demodulate the color difference signal from the chroma signal to obtain a heterodyne VTR.
Even if it is a signal, it can be directly input and demodulated without any pre-processing, and the image jitter that occurs when the VTR signal of the heterodyne system is taken in in synchronization with the subcarrier as in the past is generated. The effect is that it can be avoided. Further, there is an effect that a circuit for generating a signal synchronized with the subcarriers is not required and the circuit configuration is simplified accordingly. further,
Since the burst phase can be detected for each line, a quick response to jitter is possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of an image signal conversion apparatus according to the invention of claim 1.

FIG. 2 is a configuration diagram showing an embodiment of an image signal conversion device according to the invention described in claim 2 and an SSTV signal demodulation device according to the invention described in claim 3.

FIG. 3 is a configuration diagram showing an embodiment of an image signal conversion device according to the invention described in claim 4 and an SSTV signal demodulation device according to the invention described in claim 5.

FIG. 4 is a configuration diagram showing an embodiment of an image signal conversion device according to the invention described in claim 6 and a video signal conversion device according to the invention described in claim 7.

FIG. 5 is a vector diagram for explaining the principle of extracting a color difference signal.

[Explanation of symbols]

1 ... SSTV signal converter, 2 ... video signal converter,
4 ... AGG circuit, 9 ... Video frame memory, 10
... Composite encoder, 12 ... Write timing generator, 16 ... Voltage variable gain amplifier, 17 ... Average level detector, 21 ... Hilbert filter, 23 ... Phase angle detector, 25 ... Phase angle change detector, 31 ... Y / C
Separator, 34 ... Phase calculator, 35 ... Chroma decoder, 36 ... Matrix calculator

Claims (7)

[Claims] 1. An analog / digital converter for converting at least a low-speed scanning analog television signal into a digital signal.
An image signal conversion device comprising: a digital conversion means; and a demodulation means for demodulating image information from an output signal of the analog / digital conversion means, wherein an input level of the low speed scanning analog television signal is substantially constant. 2. An image signal converting apparatus, characterized in that input level adjusting means for setting the range is provided in front of the analog / digital converting means. 2. The input level adjusting means includes a voltage variable gain amplifier whose amplification degree is changed by an externally input gain control voltage signal, and a voltage signal corresponding to an average level of the input signal, which is a gain of the voltage variable gain amplifier. The image signal conversion apparatus according to claim 1, further comprising an average level detector that outputs as a control signal. 3. A voltage variable gain amplifier whose amplification degree changes at least according to a gain controlling voltage signal input from the outside, and a voltage signal corresponding to an average level of the input signal as a gain controlling signal of the voltage variable gain amplifier. And an average level detector for outputting the SS.
TV signal demodulator. 4. The demodulation means includes an angular frequency detection means for detecting an angular frequency of a low speed scanning television signal from an output signal of the analog / digital conversion means, and a unit of the angular frequency detected by the angular frequency detection means. 3. An image signal conversion device according to claim 1, further comprising a change amount detecting means for detecting a change amount per unit time. 5. An analog / analog converter for converting at least a low speed scanning analog television signal into a digital signal.
Digital conversion means, Hilbert conversion means for performing Hilbert conversion on the output signal of the analog / digital conversion means, and the same delay time as the input signal of the Hilbert conversion means with respect to the output signal of the analog / digital conversion means Of the output signal of the Hilbert conversion means and the output signal of the first delay means to calculate the arctangent of the output signal of the first delay means, Phase angle detecting means for generating a signal corresponding to a frequency; second delay means for delaying the output signal of the phase angle detecting means for a predetermined time; and output signal of the second delay means and the phase angle detecting means. Phase angle change detection means for detecting a frequency change of the television signal of the low-speed scanning system based on a difference from the output signal of the means. SSTV signal demodulating apparatus characterized by comprising in Bei. 6. A first analog / digital conversion means for converting at least a low speed scanning analog television signal into a digital signal, and a demodulation for demodulating image information from an output signal of the first analog / digital conversion means. Means, second analog / digital conversion means for converting the analog composite video signal into a digital signal asynchronously with the color subcarrier signal included in the video signal, and the signal of the second analog / digital conversion means is stored. In addition to holding, when a digital component video signal is input from the outside, storage holding means for rewriting the stored data to the digital component video signal, and a chroma signal component from the signal read from the storage holding means Chroma signal extracting means for extracting, and the storage A first delay means for delaying the output signal of the holding means by the same amount of delay as the delay time with respect to the input signal of the chroma signal extraction means; an output signal of the chroma signal extraction means and the first delay means. A Y / C separation means for extracting a luminance signal from the output signal, a Hilbert conversion means for performing a Hilbert conversion on the output signal of the chroma signal extraction means, and a Hilbert conversion means for the output signal of the chroma signal extraction means. Second delay means for giving the same amount of delay as the delay time with respect to the input signal, an output signal of the Y / C separation means, an output signal of the Hilbert conversion means, and an output signal of the second delay means. From the digital signal converted by the second analog / digital converting means from the burst signal included in the analog composite video signal. A color difference signal is extracted from a phase calculation unit that calculates a phase difference from the composite video signal, an output signal of the Hilbert conversion unit, an output signal of the second delay unit, and an output signal of the phase calculation unit. Chroma decoding means, matrix calculation means for calculating a component signal by matrix calculation from the output signal of the Y / C separation means and the output signal of the chroma decoding means, and outputting it to the storage holding means. An image conversion device characterized by the following. 7. An analog / digital conversion means for converting at least an analog composite video signal into a digital signal asynchronously with a color subcarrier signal included in the video signal, and storing and holding the signal of the analog / digital conversion means. At the same time, when a digital component video signal is input from the outside, a storage holding unit that rewrites the stored data to the digital component video signal, and a chroma signal component is extracted from the signal read from the storage holding unit. Chroma signal extraction means, first delay means for delaying the output signal of the memory holding means by the same amount of delay as the delay time with respect to the input signal of the chroma signal extraction means, and output signal of the chroma signal extraction means And a luminance signal from the output signal of the first delay means. Y / C separating means for outputting, Hilbert transforming means for subjecting the output signal of the chroma signal extracting means to Hilbert transform, and delay time for the output signal of the chroma signal extracting means with respect to the input signal of the Hilbert transforming means. The analog composite video signal is composed of a second delay unit that gives the same amount of delay, an output signal of the Y / C separation unit, an output signal of the Hilbert conversion unit, and an output signal of the second delay unit. Phase calculating means for calculating the phase difference between the burst signal included in the signal and the digital composite video signal digitally converted by the analog / digital converting means, the output signal of the Hilbert converting means, and the output of the second delaying means. A chroma decoding means for extracting a color difference signal from the signal and the output signal of the phase calculating means, The matrix calculation means for calculating a component signal by matrix calculation from the output signal of the Y / C separation means and the output signal of the chroma decoding means and outputting it to the storage holding means. Video signal converter.